title: Evaluation of the adjuvant effect of Salmonella-based Escherichia coli heat-labile toxin B subunits on the efficacy of a live Salmonella-delivered avian pathogenic Escherichia coli vaccine.
abstract: The present study evaluated the adjuvant effect of live attenuated salmonella organisms expressing the heat-labile toxin of Escherichia coli B subunit (LTB) on the efficacy of an avian pathogenic Escherichia coli (APEC) vaccine. The Asd(+) (aspartate semialdehyde dehydrogenase) plasmid pMMP906 containing the LTB gene was introduced into a Salmonella enterica Typhimurium strain lacking the lon, cpxR and asd genes to generate the adjuvant strain. Live recombinant Salmonella-delivered APEC vaccine candidates were used for this study. The birds were divided into three groups: group A, non-vaccinated controls; group B, immunized with vaccine candidates only; and group C, immunized with vaccine candidates and the LTB strain. The immune responses were measured and the birds were challenged at 21 days of age with a virulent APEC strain. Group C showed a significant increase in plasma IgG and intestinal IgA levels and a significantly higher lymphocyte proliferation response compared with the other groups. Upon challenge with the virulent APEC strain, group C showed effective protection whereas group B did not. We also attempted to optimize the effective dose of the adjuvant. The birds were immunized with the vaccine candidates together with 1×10⁷ or 1×10⁸ colony-forming units of the LTB strain and were subsequently challenged at 3 weeks of age. The 1×10⁷ colony-forming units of the LTB strain showed a greater adjuvant effect with increased levels of serum IgG, intestinal IgA and a potent lymphocyte proliferation response, and yielded higher protection against challenge. Overall, the LTB strain increased the efficacy of the Salmonella -delivered APEC vaccine, indicating that vaccination for APEC along with the LTB strain appears to increase the efficacy for protection against colibacillosis in broiler chickens.
authors.affiliation: College of Veterinary Medicine, Chonbuk National University, Jeonju, Republic of Korea.
authors.forename: Atul A
authors.initials: AA
authors.lastname: Chaudhari
authors.forename: John Hwa
authors.initials: JH
authors.lastname: Lee
mesh_terms: D000276:Adjuvants, Immunologic / Q000378:metabolism; D000818:Animals; D001223:Aspartate-Semialdehyde Dehydrogenase / Q000235:genetics; D001427:Bacterial Toxins / Q000378:metabolism*; D001835:Body Weight; D002645:Chickens; D004768:Enterotoxins / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D004927:Escherichia coli Infections / Q000517:prevention & control / Q000662:veterinary*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D022361:Escherichia coli Vaccines / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D007071:Immunoglobulin A, Secretory / Q000097:blood; D053308:Lymphotoxin-beta / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D011201:Poultry Diseases / Q000382:microbiology* / Q000517:prevention & control*; D012486:Salmonella typhimurium; D014613:Vaccines, Attenuated / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D000276:Adjuvants, Immunologic; D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D022361:Escherichia coli Vaccines; D007071:Immunoglobulin A, Secretory; D053308:Lymphotoxin-beta; D014613:Vaccines, Attenuated; C027538:heat-labile enterotoxin, E coli; D001223:Aspartate-Semialdehyde Dehydrogenase